physipics

TWO:

ENERGY

NOTE: These FREE Frames are samples of a much larger, and growing, collection. Neither are these presented in an unbroken sequence. The complete set, with both FREE and NOT FREE Frames provides explanation without gaps. Please scroll down to see the current FREE and NOT FREE list.

thermal energy transfers I

E1: Thermal energy transfers I

Syllabus / specification points:

• The Sun acts as a huge store of energy, emitting energy to space

The Earth has a lower temperature than the Sun, and gains energy from it

• Energy transfers from a mug of hot energy to the cooler surroundings, by thermal processes – conduction, convection and radiation

• Loss of energy by a body can cause cooling

• Energy can become thinly spread in the large surroundings; we say it is dissipated

• Objects or systems can store, gain and lose energy; energy can transfer between them

thermal energy transfers II

E2: Thermal energy transfers II

Syllabus / specification points:

• Energy natural transfers from objects or systems at higher temperature to ones at lower temperature

• Our bodies are usually at higher temperature than our surroundings, so we lose energy and we must replace it by ‘burning’ food

• We can reduce the rate of energy loss by heating the spaces we live in, thus reducing temperature difference

• We can reduce the rate of energy loss by using layers of insulation (clothing)

‘higher rate’ of emission isn’t the same as ‘more’ emission

E4.B: ‘higher rate’ of emission isn’t the same as ‘more’ emission

Syllabus / specification points:

• Emission transfers energy away from the emitting object

• An object at high temperature, such as gas in a flame, emits energy at a high rate (quickly)

• However, a cooler object that emits for a long time can, in the end, send out more energy

• The amount of energy emitted is not the same as rate of emitting

balance and imbalance of thermal energy transfer

E4.C: balance and imbalance of thermal energy transfer

Syllabus / specification points:

• The thickness of energy transfer arrows can represent RATE of energy transfer

• An object that receives energy at the same rate as it sends it out has a steady average temperature

• An object, such as a cool cake, receives energy faster than it sends it out when it is placed into a hot oven; it’s temperature then rises

• Just before the cake is taken out of the oven, when it’s fully baked, it has the same temperature as the oven

• It then emits energy at the same rate as it receives it, and its temperature is no longer changing

energy balance of a planet

E4.D: balance and imbalance of thermal energy transfer

Syllabus / specification points:

• Venus, like Earth, has a complicated atmosphere and climate.

• But over a long period of time it’s temperature is steady.

• That is because of energy balance – getting energy from the Sun and sending (emitting) energy back out into space at equal rates.

• If the temperature on Venus changes, then it emits energy faster or more slowly.

• Changes in temperature act against changes in temperature.

changing the atmosphere

E4.E: changing the atmosphere

Syllabus / specification points:

• Fossil fuels are made of very ancient plants (mostly) and animals

• Fossil fuels provide stores of energy; we burn the fuels, but that releases carbon dioxide

• The energy was stored a long time ago

• It took millions of years to create all the world’s fossil fuels

• People are using up the fuels MUCH more quickly

• That is changing our atmosphere, by adding carbon dioxide

• The Earth receives energy from the Sun

• For natural energy balance, the Earth must emit energy back into space

• Carbon dioxide is a ‘greenhouse gas’ that makes it harder for energy to escape into space

• That is destroying the natural balance of equal rates of receiving and emitting energy

changing the atmosphere, the energy balance,  the temperature, the climate

E4.F: changing the atmosphere, the energy balance, the temperature

Syllabus / specification points:

• The Earth’s temperature stays steady when there is energy balance

• The Earth is warmed by the Sun and sends energy back into space

• Extra carbon dioxide from burning fossil fuels make it harder for energy to escape through the Earth’s atmosphere

• The rate of sending energy out can be slower than the rate of receiving it

• The imbalance between ‘energy in’ and ‘energy out’ produces rise in temperature of the atmosphere

higher and higher temperature?

E4.G: higher and higher temperature?

Syllabus / specification points:

• Natural energy balance is destroyed by rapid release of carbon dioxide from burning fossil fuels

• Humans are responsible for this

• If we stop using fossil fuels now then the temperature of the Earth’s atmosphere and oceans may stop increasing (though nobody knows exactly when)

* If we keep using fossil fuels than energy imbalance will get worse (and nobody knows exactly how much the average temperature will rise)

ENERGY SPECIAL: some essential Physics of energy balance and temperature stability of oranges, cakes and planets

work and kinetic energy

E6: Work and kinetic energy

Syllabus / specification points:

• Work must be done to change motion (accelerate) and to overcome resistance to motion

• Energy is needed for doing work

• There must be a source of energy, such as fuel+oxygen; fuel may be a fossil fuel

• Moving objects have an energy store due to motion, called kinetic energy

• Energy transferred to overcome resistance becomes dissipated

how to calculate kinetic energy

EN7: how to calculate kinetic energy

Syllabus / specification points:

• An object with kinetic energy has the ability to do work on other objects with which it collides, and so it is a store of energy

• The quantity of stored energy depends on the mass of the body and its speed

• Kinetic energy = 1/2 mv2

work and extra gravitational potential energy

EN8: Work, extra height and extra gravitational potential energy

Syllabus / specification points:

• A falling object can do work, and so acts as a store of energy

• The extra energy it has due to the potential to fall is its gravitational potential energy, GPE

• At the end of a fall, the energy may become dissipated

conservation of energy

EN10: Conservation of energy

Syllabus / specification points:

• Energy cannot be destroyed

• The total energy at the end of every process is the same as at the beginning

• However, energy can become thinly spread by thermal processes, and become dissipated

conservation of energy: motion with + without resistive forces

E10.B: Conservation of energy during motion, with and without resistive forces

Syllabus / specification points:

• The total energy at the end of every process is the same as at the beginning, so if there are no resistive forces the work done by a cyclist produces a matching increase in kinetic energy

• Where there are resistive forces work must be done to overcome them, resulting in dissipation of energy

• When resistive force is the same size as the driving force all of the work done by the cyclist results in dissipation and there is no gain in kinetic energy

conservation of energy: motion without resistive forces

E10.C: Conservation of energy: falling without resistive forces

Syllabus / specification points:

• The Moon has less mass than the Earth, so has smaller gravitational field strength, g

• The total energy at the end of every process is the same as at the beginning, so if there are no resistive forces the gravitational potential energy at the start of a fall matches the kinetic energy at the end

conservation of energy: motion without resistive forces

E10.E: Conservation of energy: motion without resistive force

Syllabus / specification points:

• The total energy at the end of every process is the same as at the beginning, so if there are no resistive forces the gravitational potential energy at the highest point matches the kinetic energy at the lowest point

• A pendulum, such as a playground swing, loses and gains gravitational potential energy and kinetic energy, in turn

• When there are is no need for work to be done to overcome resistive forces then there is no dissipation

conservation of energy: motion with resistive forces

E10.F: Conservation of energy: motion with resistive force

Syllabus / specification points:

• The total energy at the end of every process is the same as at the beginning, so if there are resistive forces the gravitational potential energy at the highest point matches the total of dissipated energy plus kinetic energy at the lowest point

• There is loss of energy, by dissipation, during every swing, so the maximum gravitational potential energy and the maximum kinetic energy gradually become smaller

• A source of energy is needed to replace the dissipated energy

Energy, provisional list, July 2021

Comp: completed and ready, but so far unpublished

E1         Thermal energy transfers I                                                           FREE

E2         Thermal energy transfers II                                                          FREE

E3         Thermal energy transfers III                                                         Comp

E3.B.     Effects of gain                                                                             Comp

E4         Processes of thermal energy transfer                                         Comp

ENERGY SPECIAL: : some essential Physics of energy balance and temperature stability of oranges, cakes and planets

E4.B      ‘Higher rate’ isn’t the same as ‘more’                                         FREE

E4.C     Balance and imbalance of thermal energy transfer                     FREE

E4.D     Energy balance of a planet                                                          FREE

E4.E.     Changing the atmosphere                                                          FREE

E4.F      Changing the atmosphere, changing the energy balance          FREE

E4.G     Higher and higher temperature?                                                 FREE

E5         Work: mechanical energy transfer                                               Comp

E6         Work and kinetic energy                                                              FREE

E7         How to calculate kinetic energy                                                  FREE

E8         Work and extra gravitational potential energy                             FREE

E9         Calculating extra gravitational potential energy                          Comp

E10        Conservation of energy                                                              FREE

E10.B    Conservation of energy: motion with/without resistive force      FREE

E10.C    Conservation of energy: falling without resistive force               FREE

E10.D    Conservation of energy: falling with/without resistive force       Comp

E10.E    Conservation of energy: motion without resistive force              FREE

E10.F    Conservation of energy: motion with resistive force                   FREE

E10.G    Conservation of energy: changes of KE + GPE during orbit      Comp

E11        Energy stores                                                                             Comp

E11.B     Energy storage by stretched springs and wires                        Planned

E11.C     More energy transfers: in chemical changes                            Planned

E11.D     More energy transfers: by waves                                              Planned

E11.E     More energy transfers: in electric circuits                                  Planned

E11.F     More energy transfers: in nuclear changes                                Planned

E12        Heating water I                                                                           Comp

E13        Heating water II                                                                          Comp

E14        The snowman is melting                                                            Planned

E15        Boiling dry                                                                                  Planned

E16        Power I                                                                                       Comp

E17        Power II                                                                                      Comp

E18        Thermal conductors and thermal insulators                              Comp

E19        Reducing energy loss through a wall                                         Comp

E20        Efficiency I                                                                                  Comp

E21        Efficiency II                                                                                 Comp

E22        Efficiency III                                                                                Comp

E23        Reducing dissipation due to friction                                          Comp

E24        Coal is old                                                                                  Planned

E25        Biofuels                                                                                      Planned

E26        Water flow                                                                                  Planned

E27        Water waves                                                                              Planned

E28        Underground I                                                                            Planned

E29        Underground II                                                                           Planned

E30        Wind turbines                                                                             Planned

E31        Solar panels                                                                               Planned

E32        Solar cells                                                                                  Planned

E33        The nuclear power industry I                                                     Planned

E34        The nuclear power industry II                                                    Planned

E35        Clean energy?                                                                            Planned

All ’comp’ (completed) Frames are available at low cost.